This laboratory has been investigating genetic and biochemical changes associated with drug resistance in human tumors. We have characterized an adriamycin resistant human breast cancer cell line which has developed the phenotype of multidrug resistance. Resistance is associated with decreased drug accumulation (2-3 fold) increased activities of glutathione peroxidase (12 fold), glutathione transferase (45 fold), decreased expression of aryl hydrocarbon hydroxylase (cytochrome P-450). Using technique of in gel hybridization amplified DNA sequences have been isolated from the resistant cells and are being screened for their role in drug resistance. We have isolated cDNA clones from this resistant cell line which are amplified and overexpressed in these cells. This cDNA is homologous to a hamster gP 170 membrane glycoprotein which is often, if not always, associated with MDR in animal and human cell lines. We have also cloned the cDNA for the anionic glutathione transferase which is transcriptionally activated in the MDR MCF-7 cells. The role of the P1704 glutathione transferase in clinical drug resistance is being investigated. Other studies in our laboratory include identifying 5' and 3' DNA sequences which are involved in the regulation of dihydrofolate reductase gene expression using a human dihydrofolate reductase minigene. In addition we have developed retroviral expression vectors which can transfer drug resistance (altered dihydrofolate reductase gene) into normal cells including mouse and human bone marrow stem cells, thus protecting them from methotrexate cytotoxicity.